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4X4HO

Another loss of compression question

9 posts in this topic

I have search the forum with no luck on the remidy of this. I have an 01 426 that I just picked up and it was running great. I repacked the muffler, cleaned out the carb and rejetted it for my location. After all of that it lost compression, I can crank it over with my hand. The compression release is not stuck open so I am at a loss. What have those of you done to get it running again?

Also the valves were just checked/ adjusted by a shop about 4 months ago.

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Compression is a mechanical function, and your not going to get it running again without determining the exact cause. There are very few possibilites...

You could have a hole in the piston.

You could have a stripped / broken spark plug.

You could have stuck / burnt / out of adjustment / out of time valve(s).

You could have a severely blown head gasket.

In any case, if you've checked the plug, valves, checked the cam timing, verified the timing chain is intact, and are certain there is little or no compression, you could troubleshoot further, or since it's really simple, you could pull the head and find out what's wrong. I'd be interested to know what you find. Please, post results!

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This has happened to me a few times. If you left the fuel on, or you washed the bike, fuel or water have washed the cyllinder down. Pull the plug and drop in a few teaspoons of oil. Kick it a few times and the compression should come back.

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This has happened to me a few times. If you left the fuel on, or you washed the bike, fuel or water have washed the cyllinder down. Pull the plug and drop in a few teaspoons of oil. Kick it a few times and the compression should come back.

That is what I did and you know what it fired right up after a few kicks!

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That is what I did and you know what it fired right up after a few kicks!

My 2000 WR400 did that from time to time. I would kick it a few times and it would usually start to pop, and then the compression would come back. I also thought it was fuel washing the cylinder.

It shouldn't happen very often, if it does, take a good look at the valvespring bucket under the compression release, and make sure it is not grooved and starting to seize. It will be pretty obvious, and it can cause the valve to stay partially open causing no compression also.

Dave

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I stand corrected!:thumbsup:

I would, however, love to know how that works. Even a dry engine that's never had any oil in it will have compression. So if fuel washes the oil off the cylinder, why did that affect compression? I'm not discounting it... just very curious.:thumbsup:

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One thing you need to get in the habit of doing with these 4 strokes is to set the engine at TDC with the kick start whenever you are finished riding or storing the bike. That way all the valves are in the closed position and the valve springs are at the most relaxed position. If you just turn the bike off and push it in the corner , any condensation , especially after washing, could cause the valves to stick slightly and you will lose compression. My .02 -- WR Dave.

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One thing you need to get in the habit of doing with these 4 strokes is to set the engine at TDC with the kick start whenever you are finished riding or storing the bike. That way all the valves are in the closed position and the valve springs are at the most relaxed position. If you just turn the bike off and push it in the corner , any condensation , especially after washing, could cause the valves to stick slightly and you will lose compression. My .02 -- WR Dave.

Good point, and one I forgot about.... I know that the rings need oil to seal, and the fuel will wash down the cylinder. I know on my 400 that the bike had compression, it would just kick through very easy without using the decomp lever, SOOO I don't think you were losing all the compression in the cylinder. I think WR Dave has a better explanation than the fuel washing theory, or maybe even a combination of the two???:thumbsup:

Dave

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This may have just happened to me. My 426 has been runninng awesome for years!!! After my ride on Saturday, I gave the bike a good wash. Afterwards, I couldn't get it started. I took the tank off and found the spark plug wiring to be disengaged! I pushed it back in, but the bike still wouldn't start. I'm going to have to do some more troubleshooting. But the valves sticking due to the wash may be an appropriate theory.

Another tid bit of information. Washing the bike usually only takes a few minutes for me. This last time the kids and family kept distracting me, so it took an hour or two. That may have allowed the water to sit in the engine longer before restarting to burn it out.

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